I am trying to send a Thank You email to our donor contributors through CiviMail. We have a message template set up. But our test emails keep showing the wrong sender email account "firstname.lastname@example.org" instead of our goal "email@example.com." The latter email address is already set up in our From Email Address and Mail Accounts. The CiviCRM manual mentioned that there was a dropdown to change the sender? But I don't see this option anywhere. Please advise.